A known cylinder is provided with a permanent magnet on a piston unit, which reciprocates together with a piston rod in a cylinder tube such as a hydraulic cylinder, and a magnetic sensor on the exterior of the cylinder tube to detect magnetism passing through the magnetic sensor, thereby measuring a cylinder stroke position.
For example, Patent Literature 1 discloses a cylinder including a rotary encoder, provided on a cylinder head, for detecting the amount of reciprocating motion of the piston rod as the amount of rotation and a resetting magnetic sensor on the middle portion of the outer periphery of a tube. The resetting magnetic sensor detects the magnetism generated by a magnet secured on the piston unit reciprocating in the tube and resets the measured position obtained from the value detected by the rotary encoder to an origin position when the a peak value of magnetism is detected.
Patent Literature 2 discloses a cylinder including a piston which reciprocates in the cylinder, a communication hole penetrating the piston in the direction of the reciprocating motion of the piston, and a check valve connected to the communication hole. A valve body of the check valve opens when the piston moves to a stroke end position of the piston to absorb the shock made by the piston making contact with the stroke end.